The air/fuel ratio used during the operation of a combustion appliance can affect the efficiency and emissions of the combustion appliance. Examples of such combustion appliances include furnaces, water heaters, boilers, direct/in-direct make-up air heaters, power/jet burners and any other residential, commercial or industrial combustion appliance. In many cases, a combustion appliance can be modulated over a plurality of burner loads, with each burner load resulting in a different heat output. At higher burner loads, more fuel and more air are provided to the burner, and at lower burner loads less fuel and less air are provided to the burner.
In many cases, the combustion appliance may include a burner that is fed air by a modulating blower or the like and fuel is fed by a modulating gas valve. The modulating gas valve may have an air/fuel controller that is designed to control the air/fuel ratio that is delivered to the burner. In some cases, the air/fuel controller may not have direct control over the burner load of the combustion appliance. Instead, the air/fuel controller may be a slave device and simply receive a burner load command from an external controller, and may respond by modulating the gas valve to provide a desired air/fuel ratio to the burner at the commanded burner load. For increased efficiency and/or reduced emissions, the air/fuel ratio may be set higher at lower burner loads and lower at higher burner loads.
In many cases, an air/fuel ratio versus burner load curve is set during a commissioning process of the gas valve at the time of installation or during subsequent maintenance. The particular air/fuel ratio versus burner load curve may depend on the particular equipment involved and/or the particular application at hand. Air/fuel ratio curve versus burner load curve commissioning can be a time consuming and tedious process, especially when the air/fuel controller does not control the burner load of the combustion appliance. What would be desirable are improved methods and systems for commissioning an air/fuel curve of a combustion appliance.